It's interesting. It's been 12+ years, so I might be mis-remembering that detail, but it's funny how there's such a correlation regarding the topics to which you'll chime in on to "correct" assertions -- Those who are showing support for Joe Paterno, and those who are throwing shade in the direction of the University of Michigan.
Even if it was first down, those free, unearned, extra 12-15 yards, with such little time on the clock, were massively significant.
One thing that is also interesting -- you "mis-remembered" the detail such that it put Michigan in the worst possible position (4th-and-long) to convert the first down and extend the game.
Besides, as I've shown before --- the call that the play was a complete pass, based on the rulebook as it stood at that time (2005), was not incorrect. (based on the rulebook from 2008 forward, it's an incorrect pass).